Plastic containers, for example plastic bottles, are usually produced with so-called blow molding machines. In such blow molding machines, plastic preforms, which have been heated before in a temperature control means, are shaped in blow molds to give the desired plastic containers. For this, the preforms are subjected to compressed air in the blow molds.
Thermal conditioning of the preforms in a temperature control means upstream of the blow molding machine is necessary to make the plastic material of the preforms moldable. To ensure constant quality of the produced plastic containers, the preforms must have an exactly defined temperature during the blow molding process.
Usually, the preforms are manufactured beforehand as molded parts, that means in an injection molding process. In this case, it is advantageous to manufacture the preforms in a clocked process where several preforms are manufactured simultaneously in one injection molding operation. A clocked injection molding machine can also be connected in a block with a blow molding machine to combine the manufacturing process of the preforms and the plastic containers. Such a block system is known, for example, from DE 697 12 130.
If a clocked injection molding machine is connected in a block with a continuously working stretch-blow molding machine, more precisely is operated with a blow-molding unit and a temperature control means in a blocked connection, the simultaneously manufactured preforms, however, first must be brought into a line such that they can then be introduced into the temperature control means. By this, the preforms that are the last ones to be introduced into the temperature control means usually have a lower temperature than the preforms that have been introduced before them. Other factors, such as, for example, the mold temperatures in injection molding, can lead to varying temperatures of the produced preforms.
Such a different or varying temperature of the preforms can lead to a varying quality of the manufactured plastic containers.